Positive electrodes for lithium batteries

ABSTRACT

This invention provides lithium-rich compounds as precursors for positive electrodes for lithium cells and batteries. The precursors comprise a Li 2 O-containing compound as one component, and a second charged or partially-charged component, selected preferably from a metal oxide, a lithium-metal-oxide, a metal phosphate or metal sulfate compound. Li 2 O is extracted from the above-mentioned electrode precursors to activate the electrode either by electrochemical methods or by chemical methods. The invention also extends to methods for synthesizing and activating the precursor electrodes and to cells and batteries containing such electrodes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 60/994,874, filed on Sep. 21, 2007, which is incorporated herein byreference in its entirety.

CONTRACTUAL ORIGIN OF THE INVENTION

The United States Government has rights in this invention pursuant toContract No. W-31-109-ENG-38 between the United States Government andThe University of Chicago and/or pursuant to Contract No.DE-AC02-06CH11357 between the United States Government and UChicagoArgonne, LLC representing Argonne National Laboratory.

FIELD OF THE INVENTION

This invention relates to positive electrodes (cathodes) for lithiumcells and batteries, notably rechargeable lithium-ion cells andbatteries. These batteries are used to provide power for a wide range ofapplications such as portable telecommunications equipment, computers,medical devices, electric vehicles, and hybrid-electric vehicles.

BACKGROUND OF THE INVENTION

Electrochemical energy conversion and storage in new, advanced batterysystems will undoubtedly contribute to finding solutions to the world'senergy problems and, in particular, to lessening its dependence onfossil fuels for transportation. Non-aqueous, lithium batteries offerthe most flexible chemistries and the best promise forgreater-than-incremental improvement over known battery systems,particularly in terms of their practical energy and power performance.

The most significant advantage of lithium batteries over aqueous systemsis that they can operate at voltages significantly higher than thedecomposition potential of water (about 1.2 V). Despite the progressthat has been made in recent years with conventional Li_(x)C₆/LiCoO₂cells that operate at about 4 V, the energy and power densities ofrechargeable lithium-ion batteries for the mass storage of energy, e.g.,for large scale applications such as electric vehicles and plug-inhybrid electric vehicles, are still limited by the specific andvolumetric capacities of the electrode materials currently in use. Newmaterials are required to advance lithium battery technology. Thepresent invention provides novel positive electrode (cathode) materials,for a future generation of lithium electrochemical cells and batteries.The invention also provides examples of such electrode materials,methods for synthesizing the electrodes, and evaluating the electrodesin non-aqueous lithium cells.

SUMMARY OF THE INVENTION

This invention relates to materials that can be used as precursors forpositive electrodes in non-aqueous lithium cells and batteries,preferably rechargeable lithium-ion cells and batteries, and to thepositive electrodes formed therefrom. More specifically, the inventionrelates to precursor materials for positive electrodes containinglithium cations, other metal cations, and charge balancing anions. Theprecursor material comprises a first component, containing one or moreLi₂O-containing materials such as those with Mn, V, Fe and Ti cations,for example, Li₂MnO₃ (Li₂O.MnO₂), LiV₃O₈ (Li₂O.3V₂O₅), Li₃VO₄(3Li₂O.V₂O₅) LiFe₅O₈ (Li₂O.2.5Fe₂O₃), LiFeO₂ (Li₂O.Fe₂O₃), Li₅FeO₄(5Li₂O.Fe₂O₃), Li₂TiO₃ (Li₂O.TiO₂; Li:Ti=2:1), Alternatively, the firstcomponent may comprise an intergrown material having a compositestructure or a blended material, in which the intergrown or blendedmaterials each include two or more Li₂O-containing components ofdifferent molecular structure, such as Li₂MnO₃.LiMO₂ where M comprises ametal cation, typically one or more transition metal cations such as Mn,Ni and/or Co cations, or the first component may comprise structurallyintegrated or blended Li₂MnO₃.LiM′₂O₄ compounds where M′ typicallycomprises one or more metal cations, such as Li and Mn cations. Theelectrode precursor materials also comprise a second component,containing one or more charged or partially-charged electrode compoundsthat can react with an integral or fractional molar quantity of lithium,based on the molecular formula of the charged material and partiallycharged material respectively, during the charging and discharging ofthe electrode when included in an electrochemical cell, preferably, butnot exclusively, selected from a metal oxide, a lithium metal oxide, ametal phosphate, or a metal sulfate, such as MnO₂, V₂O₅, Li_(1+x) V₃O₈(O≦x≦0.3), Fe₂O₃, Fe_(1−y)PO₄ (0≦y≦1) or Fe₂(SO₄)₃, with the provisothat at least one of the electrode components does not containmanganese. The second component may also be a Li₂O-containing compoundsuch as LiV₃O₈ (Li₂O.3V₂O₅) that represents an example of a chargedelectrode compound that can react with lithium to form Li₄V₃O₈.According to the invention, Li₂O is extracted from the above-mentionedelectrode precursors to activate the electrode either directly byelectrochemical methods by applying a sufficiently high potential in anelectrochemical cell, or by chemical methods, e.g., by reaction with anacidic medium having a 0<pH<7. The present invention also encompassesmethods for synthesizing the precursor lithium-metal-oxide electrodes,as well as lithium cells and batteries containing such precursorelectrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention comprises certain novel features hereinafter fullydescribed, and illustrated in the accompanying drawings, it beingunderstood that various changes in the details may be made withoutdeparting from the spirit, or sacrificing any of the advantages of thepresent invention.

FIG. 1 is an illustration of the powder X-ray diffraction pattern of acomposite 0.74Li₂MnO₃.0.26Li_(1.2)V₃O₈ electrode powder prepared at 300°C.

FIG. 2 is a graphical representation of the relationship between thevoltage and capacity for an initial charge and subsequentdischarge/cycles of a Li/0.74Li₂MnO₃.0.26Li_(1.2)V₃O₈ cell operated atroom temperature.

FIG. 3 is a graphical representation of the relationship between thevoltage and capacity for an initial discharge and subsequentcharge/discharge cycle of a Li/0.74Li₂MnO₃.0.26Li_(1.2)V₃O₈ celloperated at room temperature.

FIG. 4 is a graphical representation of the relationship between thevoltage and capacity for an initial charge and subsequentdischarge/charge cycles of a C₆/0.74Li₂MnO₃.0.26Li_(1.2)V₃O₈ celloperated at room temperature.

FIG. 5 is an illustration of the powder X-ray diffraction pattern of acompositeLi/0.9(0.5Li₂MnO₃.0.5LiNi_(0.44)Co_(0.25)Mn_(0.31)O₂).0.1Li_(1.2)V₃O₈electrode powder prepared at 450° C.

FIG. 6 is a graphical representation of a) the relationship between thevoltage and capacity for an initial charge and subsequentdischarge/charge cycles of aLi/0.9(0.5Li₂MnO₃.0.5LiNi_(0.44)Co_(0.25)Mn_(0.31)O₂).0.1Li_(1.2)V₃O₈cell operated at room temperature, and b) a capacity vs. cycle numberplot of the same cell for 50 cycles.

FIG. 7 is an illustration of the powder X-ray diffraction pattern of acomposite xLi₅FeO₄.(1−x)LiFeO₂ (0.5≦x≦0.6) electrode powder prepared at900° C.

FIG. 8 is a graphical representation of the relationship between thevoltage and capacity for an initial charge and subsequent discharge of aLi/xLi₅FeO₄.(1−x)LiFeO₂ (0.5≦x≦0.6) cell operated at room temperature.

FIG. 9 is a graphical representation of the relationship between thevoltage and capacity for the initial discharge and second charge of aLi/xLi₅FeO₄.(1−x)LiFeO₂ cell operated at room temperature.

FIG. 10 is a graphical representation of the relationship between thevoltage and capacity for an initial charge and subsequent threedischarge/charge cycles of a C₆/Li₅FeO₄.FePO₄ cell operated at roomtemperature.

FIG. 11 is a graphical representation of a) the relationship between thevoltage and time for an initial charge and subsequent discharge of aC₆/Li₅FeO₄.Li_(1.2)V₃O₈ cell operated at room temperature, and b) therelationship between voltage and capacity for the subsequent sixdischarge cycles.

FIG. 12 is a schematic representation of an electrochemical cell.

FIG. 13 is a schematic representation of a battery consisting of aplurality of cells connected electrically in series and in parallel.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

State-of-the-art Li_(x)C₆/LiCoO₂ lithium-ion batteries are limited bythe theoretical specific capacity of the graphite anode (about 372mAh/g) and LiCoO₂ cathode (about 280 mAh/g). In practice, the graphiteanode provides approximately 300-350 mAh/g, while the LiCoO₂ cathodeprovides only approximately 130-140 mAh/g. By contrast, lithium metal ora metal anode that alloys with lithium, such as Sn, offers asignificantly higher theoretical capacity than a graphite anode (about3863 mAh/g for lithium and 994 mAh/g for Sn). In addition, therelatively high density of metal alloys, typically ρ>4 g/cm³, providesanodes with significantly higher volumetric capacity compared tographite (ρ=2.2 g/cm³). Manganese and vanadium oxide cathodes, such asMnO₂, V₂O₅ and LiV₃O₈ (Li₂O.3V₂O₅), which can be used directly ascathodes in the charged state, offer theoretical capacities in the rangeof about 300-440 mAh/g, respectively, of which approximately 250-300mAh/g has been realized in practice. In addition, manganese-basedelectrodes with integrated or blended composite structures, such as‘layered-layered’ xLi₂MnO₃.(1−x)LiMO₂ (e.g., M=Mn, Ni, Co) structures,as disclosed by Kim et al. in Chemistry of Materials, Volume 16, page1996 (2004), and ‘layered-spinel’ xLi₂MnO₃.(1−x)LiMn_(2−y)M_(y)O₄ (e.g.,M=Li, Ni, Co, Mg, Al) structures, as disclosed in U.S. Pat. No.7,303,840, the entire disclosures of which are incorporated byreference, have been reported to yield capacities close to 250 mAh/g atrelatively low current rates. In U.S. Pat. No. 7,303,840, thelayered-spinel components have a Li₂O-containing component (Li₂MnO₃) anda partially charged spinel component (LiMn_(2−y)M_(y)O₄) but falloutside the scope of this invention because both components contain Mn.

In principle, the lithium cells with the electrode components of thisinvention can significantly increase the capacity and energy deliveredby conventional lithium-ion cells that are assembled in the dischargedstate. In one embodiment of the invention, new positive electrode(cathode) precursor materials for lithium cells are disclosed, notablythose containing at least one component from which Li₂O can beextracted, either electrochemically or chemically, in combination withone or more charged electrode components, the Li₂O-containing componentbeing used to activate and enhance the capacity of the electrode.Broadly speaking, the invention relates to positive electrode precursorscontaining surplus lithium that can be extracted electrochemically athigh potentials to load carbon-, metal-, semi-metal-, intermetallic-,and metal oxide anode materials, such as graphite, Sn, Si, Cu₆Sn₅ andLi₄Ti₅O₁₂ materials, respectively, with lithium during the initialcharging process, the lithiated anode materials being able to providesufficient lithium on the subsequent discharge to both the activatedelectrode component and to the charged electrode component contained inthe initial parent precursor electrode.

When lithium is extracted from the precursor electrode as Li₂O, bothlithium ions and oxygen are released from the electrode during theactivation of the electrode. This activation reaction leaves astructurally modified electrode that can accommodate lithium on thesubsequent discharge. The activated electrode may be crystalline and mayshow a close crystallographic relationship to parent precursor material.Alternatively, the activated electrode may be poorly crystalline oramorphous to X-rays.

In a second embodiment, the invention relates to precursor materials forpositive electrodes containing lithium and other metal cations andcharge balancing anions, that contain, as a first component, one or moreLi₂O-containing compounds such as those with Mn, Fe, and V cations.Lithium-manganese-oxides and lithium-iron-oxide compounds, inparticular, have the advantages of being low cost and environmentallybenign materials; vanadium oxides and lithium-vanadium-oxide compoundsoffer high electrochemical capacities compared to other transition metaloxide compounds. The first component of the precursor electrodematerials of this invention have a lithium to metal (Li:M) ratio greaterthan, equal to, or less than 1:1, for example, Li₂MnO₃ (Li₂O.MnO₂,Li:Mn=2:1), LiV₃O₈ (Li₂O.3V₂O₅, Li:V=1:3), Li₃VO₄ (3Li₂O.V₂O₅,Li:V=3:1), Li₅FeO₈ (Li₂O.5Fe₂O₃, Li:Fe=1:5), LiFeO₂ (Li₂O.Fe₂O₃,Li:Fe=1:1), Li₅FeO₄ (5Li₂O.Fe₂O₃, Li:Fe=5:1), Li₂TiO₃ (Li₂O.TiO₂;Li:Ti=2:1). The first component may, alternatively, comprise intergrowncompounds with composite structures or blended compounds containing theLi₂O-containing component, such as layered Li₂MnO₃.LiMO₂ materials inwhich M is typically a transition metal cation, such as Mn, Ni, Co,optionally in combination with one or more other metal cations such asAl and Mg, or the first component may comprise structurally integratedor blended Li₂MnO₃.LiM′₂O₄ (‘layered-spinel’) materials in which M′ istypically comprised of Li and Mn, optionally in combination with one ormore other metal cations such as Ni, Co, Mg, and Al. Alternatively, thestructurally-integrated or blended component may be more complex, suchas a three-component xLi₂MnO₃.yLiMO₂zLiM₂O₄ (x+y+z=1) or a higher ordersystem. The electrode precursor materials of this invention comprise, asa second component, one or more electrode materials in either a chargedor partially-charged state. Such charged and partially charged materialsare well known in the art to be able to react electrochemically withlithium, for example, by a displacement reaction or by accommodatinglithium within its structure, the second component being selectedpreferably, but not exclusively, from a metal oxide, a lithium metaloxide, a metal phosphate, or a metal sulfate, such as MnO₂, V₂O₅,Li_(1+x)V₃O₈ (0≦x≦0.3), Fe₂O₃, Fe_(1−y)PO₄ (0≦y≦1) or Fe₂(SO₄)₃, withthe proviso that at least one of the electrode components does notcontain manganese. The second component can also be a Li₂O-containingmaterial, such as LiV₃O₈ (Li₂O.3V₂O₅), which is an example of a chargedcathode that can react electrochemically with lithium by accommodatingat least three lithium ions within its structure to form Li₄V₃O₈ asreported by de Picciotto et al in Solid State Ionics, Volume 62, page297 (1993). On the other hand, the composition Li_(1.2)V₃O₈ is anexample of a partially charged cathode material because it is possibleto extract 0.2 lithium ions to reach its fully charged state LiV₃O₈(Li₂O.3V₂O₅). Likewise, MnO₂ is an example of a fully charged electrodematerial that can react with one lithium to form LiMnO₂ and Li_(0.5)MnO₂(or LiMn₂O₄ spinel) represents an example of a partially charged cathodebecause it can react with 0.5 lithium ions to form LiMnO₂ and because0.5 lithium ions can also be extracted from Li_(0.5)MnO₂ to produce thefully charged electrode material MnO₂. The charged electrode componentsof the electrode precursors of this invention should preferably providea capacity of at least 100 mAh/g in a lithium electrochemical cell,whereas the partially charged electrode materials should provide acapacity of at least 50 mAh/g in the cell.

In a third embodiment of this invention, the Li₂O constituent of theLi₂O-containing components is extracted from the electrode precursors toactivate the electrode either directly by electrochemical methods at asufficiently high potential in an electrochemical cell or by chemicalmethods, e.g., by reaction with an acidic solution having a 0<pH<7 priorto loading the electrode in a fully-charged or partially charged cell.The acid may be either an inorganic acid or an organic acid, preferablyan inorganic acid comprising HF, HCl, HNO₃ or H₃PO₄. When the Li₂Ocomponent is extracted electrochemically from the positive electrode,the lithium ions are removed with the concomitant release of oxygen thatcan either evolve as a gas or react with the surrounding electrolyte.The principal advantage of this invention is that the Li₂O component ofthe positive electrode precursor can act as a source of surplus lithiumto load a negative electrode during the activation step and that thislithium can be used during a subsequent discharge reaction not only withthe host electrode component from whence it came, but also with thecharged or partially charged components in the parent electrode that aresusceptible to reaction with lithium, as described hereinbefore, therebymaximizing the use and capacity of the overall electrode.

The present invention encompasses methods for synthesizing the precursorpositive electrodes, as well as electrochemical lithium cells andbatteries containing such precursor electrodes.

The principles of this invention are described with respect to thefollowing idealized reactions:

-   -   1. Composition of precursor electrode: Li₂MnO₃:2 Li_(1.2)V₃O₈,        -   Initial charge reaction at the electrode:

Li₂MnO₃+2 Li_(1.2)V₃O₈→MnO₂+3 V₂O₅+4.4 Li⁺+O₂+4.4 e⁻

-   -   -   Subsequent discharge reaction:

4.4 Li⁺+MnO₂+3 V₂O₅+4.4 e⁻→LiMnO₂+3 Li_(1.33)V₂O₅.

-   -   2. Composition of precursor electrode: 4 Li₅FeO₄:18 Fe₂O₃        -   Initial charge reaction at the electrode:

4 Li₅FeO₄+18 Fe₂O₃→20 Fe₂O₃+20 Li⁺+5 O₂+20 e⁻

-   -   -   Subsequent discharge reaction:

20 Li⁺+20 Fe₂O₃+20 e⁻→20 LiFe₂O₃.

-   -   3. Composition of precursor electrode:        Li₂MnO₃.LiMn_(0.5)Ni_(0.5)O₂+2 Li_(1.2)V₃O₈        -   Initial charge reaction at the electrode:

Li₂MnO₃.LiMn_(0.5)Ni_(0.5)O₂+2 Li_(1.2)V₃O₈→

MnO₂.Mn_(0.5)Ni_(0.5)O₂+3 V₂O₅+5.4 Li⁺+O₂+5.4 e⁻

-   -   -   Subsequent discharge reaction:

5.4 Li⁺+MnO₂.Mn_(0.5)Ni_(0.5)O₂+3 V₂O₅+5.4 e⁻→

LiMnO₂.LiMn_(0.5)Ni_(0.5)O₂+3 Li_(1.133)V₂O₅.

-   -   4. Composition of precursor electrode:        Li₂MnO₃.LiMn_(0.5)Ni_(0.5)O₂+FePO₄        -   Initial charge reaction at the electrode:

Li₂MnO₃.LiMn_(0.5)Ni_(0.5)O₂+FePO₄→

MnO₂.Mn_(0.5)Ni_(0.5)O₂+3.0 Li⁺+FePO₄+½ O₂+3.0 e⁻

-   -   -   Subsequent discharge reaction:

3.0 Li⁺+MnO₂.Mn_(0.5)Ni_(0.5)O₂+FePO₄+3.0 e⁻→

LiMnO₂.LiMn_(0.5)Ni_(0.5)O₂+LiFePO₄.

The overall principles of the invention are demonstrated by thefollowing practical examples:

EXAMPLE 1

A positive electrode precursor with the nominal composition0.74Li₂MnO₃.0.26Li_(1.2)V₃O₈ was prepared by intimately mixingindividually-prepared Li₂MnO₃ and Li_(1.2)V₃O₈ powders in the desiredstoichiometric ratio and subsequently heating the mixture at about 300°C. in air for 24 hours. The Li_(1.2)V₃O₈ precursor was prepared bymixing Li₂CO₃ and NH₄VO₃ powders and thereafter calcining them at about450° C. for 48 hours in air. The Li₂MnO₃ precursor sample was preparedby mixing and calcining Li₂CO₃ and MnCO₃ powders under the samepreparative conditions as the Li_(1.2)V₃O₈ sample. The X-ray diffractionpattern of the 0.74Li₂MnO₃.0.26Li_(1.2)V₃O₈ product is shown in FIG. 1.

Electrochemical tests of the 0.74Li₂MnO₃.0.26Li_(1.2)V₃O₈ electrodeswere conducted in lithium ‘half’ cells as follows. The electrodes foreach lithium cell were fabricated from a mixture of 84 wt % of0.74Li₂MnO₃.0.26Li_(1.2)V₃O₈ electrode powder, 8 wt % polyvinylidenedifluoride (PVDF) polymer binder (Kynar, Elf-Atochem), 4 wt % acetyleneblack (Cabot), and 4 wt % graphite (SFG-6, Timcal) slurried in1-methyl-2-pyrrolidinone (NMP) (Aldrich, 99+%). An electrode laminatewas cast from the slurry onto an Al current collector foil using adoctor-blade. The laminate was subsequently dried, first at about 75° C.for about 10 hours, and thereafter under vacuum at about 70° C. forabout 12 hours. The electrolyte was 1 M LiPF₆ in a 1:1 mixture ofethylene carbonate (EC) and ethylmethyl carbonate (EMC). The electrodeswere evaluated at room temperature in coin-type cells (size CR2032,Hohsen) with a lithium foil counter electrode (FMC Corporation, LithiumDivision) and a polypropylene separator (Celgard 2400). Cells wereassembled inside a He-filled glovebox (<5 ppm, H₂O and O₂) and cycled ona Maccor Series 2000 tester under galvanostatic mode using a constantcurrent density of about 0.05 mA/cm² between 4.8 and 2.0 V.

The voltage profiles of the first two charge/discharge cycles of aLi/0.74Li₂MnO₃.0.26Li_(1.2)V₃O₈ cell, cycled between 4.8 and 2.0 V areshown in FIG. 2, whereas the voltage profiles of an identical cell thatwas discharged first, followed by one charge/discharge cycle between thesame voltage limits are shown in FIG. 3. In FIG. 2, the capacitywithdrawn from the 0.74Li₂MnO₃.0.26Li_(1.2)V₃O₈ electrode between 3.3and 4.0 V on the initial charge is attributed to the extraction of Lifrom the Li_(1.2)V₃O₈ component with a concomitant oxidation of V⁴⁺ toV⁵⁺; the capacity withdrawn from the electrode above 4.0 V is attributedto the irreversible extraction of Li₂O from the Li₂MnO₃ component thatyields an electrochemically active MnO₂ component that can accommodatelithium within its structure on the subsequent discharge. The voltageprofile of the second charge process differs significantly from thefirst charge process (FIG. 2) as a result of the activation of theprecursor electrode, whereas the profile of the second discharge closelyfollows that of the first, reflecting the reversibility of the activatedelectrode reaction. The capacity delivered between 4.5 and about 3.0 Vis attributed predominantly to the MnO₂ component of the electrode,whereas the capacity delivered in a series of steps between 3.0 and 2.0V is attributed predominantly to the vanadium oxide component of theelectrode. FIG. 3 demonstrates that when a similar cell is initiallydischarged (discharge 1), lithium is inserted only into the Li_(1.2)V₃O₈component, not the unactivated Li₂MnO₃ component, and that activation ofthe Li₂MnO₃ component occurs on the subsequent charge. Thereafter, thecell discharges in a like manner to that shown in FIG. 2. FIGS. 2 and 3demonstrate that a high electrochemical discharge capacity ofapproximately 250 mAh/g can be obtained from0.74Li₂MnO₃.0.26Li_(1.2)V₃O₈ electrode precursors when activated to 4.8V and subsequently cycled to 2.0 V in a lithium cell. This capacity issignificantly higher than the capacity obtained in practice fromconventional LiCoO₂ (layered), LiMn₂O₄ (spinel) and LiFePO₄ (olivine)electrodes.

EXAMPLE 2

The 0.74Li₂MnO₃.0.26Li_(1.2)V₃O₈ electrodes of Example 1 were alsoevaluated in lithium-ion ‘full’ cells containing MCMB graphitic anodes.Cells were cathode limited. The cells were cycled between 4.7 and 1.0 Vat 0.05 mA/cm². The voltage profiles of the initial charge andsubsequent discharge/charge cycles of a typical cell are shown in FIG.4, which demonstrates the reversibility of the activated0.74Li₂MnO₃.0.26Li_(1.2)V₃O₈ electrodes in a lithium-ion cellconfiguration. The relatively low rechargeable capacity obtained fromthe positive electrode (approximately 150 mAh/g) is attributed to theexcess MCMB graphite that was used in the unbalanced cell and to therelatively high Li₂MnO₃ content in the electrode. Improvements in theelectrode capacity and cycling efficiency can be expected by increasingthe Li_(1.2)V₃O₈ content in the electrode relative to Li₂MnO₃, and bybalancing the required relative amounts of anode and cathode materialsin the lithium-ion cell.

EXAMPLE 3

In this example, a precursor material, consisting of a Li₂O-containing0.5Li₂MnO₃.0.5LiNi_(0.44)Co_(0.25)Mn_(0.31)O₂ component(Li₂MnO₃═Li₂O.MnO₂) and a charged Li_(1.2)V₃O₈ component in a 0.9:1molar ratio was evaluated. The0.9(0.5Li₂MnO₃.0.5LiNi_(0.44)Co_(0.25)Mn_(0.31)O₂).0.1Li_(1.2)V₃O₈precursor was prepared by mixing pre-prepared0.5Li₂MnO₃.0.5LiNi_(0.44)Co_(0.25)Mn_(0.31)O₂ and 0.1Li_(1.2)V₃O₈materials in a 0.9:01 stoichiometric ratio and heating them typically ata temperature in the range of about 100° C. to 450° C. for about 12hours in air. The 0.5Li₂MnO₃.0.5LiNi_(0.44)Co_(0.25)Mn_(0.31)O₂component was prepared by first intimately mixing Li₂CO₃ and(Mn_(0.656)Co_(0.125)Ni_(0.219))(OH)₂ powders and, thereafter, calciningthe mixture at about 700° C. for about 36 h in air. The Li_(1.2)V₃O₈precursor was prepared as described in Example 1. The X-ray diffractionpattern of0.9(0.5Li₂MnO₃.0.5LiNi_(0.44)Co_(0.25)Mn_(0.31)O₂).0.1Li_(1.2)V₃O₈product was consistent with the typical patterns of0.5Li₂MnO₃.0.5LiNi_(0.44)Co_(0.25)Mn_(0.31)O₂ and Li_(1.2)V₃O₈materials. When heated to about 450° C., the diffraction pattern of theproduct showed, in addition, a minor amount of an unidentifiedby-product of the reaction (FIG. 5). FIG. 6 a shows the initial chargeand subsequent discharge/charge profiles of aLi/0.9(0.5Li₂MnO₃.0.5LiNi_(0.44)Co_(0.25)Mn_(0.31)O₂).0.1Li_(1.2)V₃O₈cell cycled between 4.6 and 2.0 V at 0.05 mA/cm² at room temperature.FIG. 6 b demonstrates, in a capacity vs. cycle number plot, that arechargeable capacity greater than 200 mAh/g was delivered for 50cycles, which is significantly higher than the capacity that can beachieved from state-of-the-art LiCoO₂, LiMn₂O₄ and LiFePO₄ electrodes,in accordance with the principles of this invention.

EXAMPLE 4

This example demonstrates that an iron-based precursor material,consisting of a Li₅FeO₄ (5Li₂O.Fe₂O₃) component and a LiFeO₂ component(Li₂O.Fe₂O₃), represented generically in two-component notation asxLi₅FeO₄.(1−x)LiFeO₂ (0<x<1) can be used effectively as an electrodeprecursor and source of lithium for charging lithium cells. ThexLi₅FeO₄.(1−x)LiFeO₂ precursor was prepared by the reaction of lithiumoxide powder (Li₂O; Aldrich, 99+%) and iron oxide powder (Fe₂O₃, Aldrich99.9%). The powders were mixed using a mortar and pestle, and then firedat about 750° C. under nitrogen for about 12 hours. The product wasre-ground, pelletized and re-fired under nitrogen at about 900° C. forseveral hours. The two-component character of this precursor wasconfirmed by powder X-ray diffraction (CuKα radiation) (FIG. 7). Aquantitative analysis of the diffraction pattern revealed that theproduct contained approximately 40 to 50% LiFeO₂ and 50 to 60% Li₅FeO₄.FIG. 8 demonstrates that the electrochemical extraction of lithium fromthe xLi₅FeO₄.(1−x)LiFeO₂ (0.5≦x<0.6) precursor in a lithium cell,assembled according to the methods described in Examples 1, 2 and 3, andcycled between 5.0 and 1.5 V at 0.05 mA/cm², occurs in a two-stepprocess, consistent with the two-component character of the precursormaterial, the first process occurring at a lower potential (about 4.0 Vvs. Li/Li⁺) than the extraction of lithium from the Li₂MnO₃ component ofthe corresponding 0.74Li₂MnO₃.0.26Li_(1.2)V₃O₈ electrode precursor inFIG. 2 (>4.5 V vs. Li/Li⁺). The large irreversible capacity loss thatoccurs on the initial cycle is attributed to the surplus of lithium thatcan be withdrawn from the xLi₅FeO₄.(1−x)LiFeO₂ precursor electrodeduring charge (443 mAh/g) and the relatively small quantity of lithiumthat could be introduced into the activated Fe₂O₃ electrode component onthe subsequent discharge (112 mAh/g) (FIG. 8). This phenomenon can beunderstood by considering a xLi₅FeO₄.(1−x)LiFeO₂ electrode that containsequimolar amounts of Li₅FeO₄ (Li₂O.Fe₂O₃) and LiFeO₂ (Li₂O.Fe₂O₃) (i.e.,x=0.5). Such an electrode would yield a theoretical capacity of 645mAh/g during charge if all the Li₂O was withdrawn from the twocomponents, but would deliver a theoretical capacity of only 215 mAh/gif the resulting activated Fe₂O₃ electrode was completely discharged toLiFe₂O₃. Essentially all the capacity of the Li/xLi₅FeO₄.(1−x)LiFeO₂electrode of this Example that was delivered on the initial dischargecould be recovered on the second charge to 4.8 V, reflecting thereversible redox chemistry of the Fe³⁺/Fe²⁺ couple in the electrode(FIG. 9). Such iron-based electrodes with a high Li₂O content thereforehave particular utility in composite electrode systems that also containan appreciable amount of an uncharged, high capacity component in theelectrode precursor, such as V₂O₅, LiV₃O₈ and MnO₂, and for supplyinghigh capacity anode materials with sufficient lithium to offsetirreversible capacity phenomena, as often observed in metal, semi metaland intermetallic electrode systems.

EXAMPLE 5

A charged FePO₄ precursor electrode component was synthesized from acommercial LiFePO₄ (olivine) sample. The LiFePO₄ sample was chemicallydelithiated with a 2-fold excess of NO₂BF₄ in an acetonitrile solvent.The powder was isolated by suction filtration and washed multiple timeswith fresh acetonitrile. Lithium full cells (lithium-ion configuration)were constructed with a graphite (MCMB) anode and a cathode ofphysically blended Li₅FeO₄.FePO₄ materials in a 1:1 molar ratio. Thecathode compartment consisted of 80% Li₅FeO₄.FePO₄, 8% PVDF binder, and6% graphite and 6% acetylene black as current collecting media. Theelectrolyte consisted of a 1.2 M LiPF₆ solution in ethylene carbonate:ethylmethyl carbonate (3:7 molar ratio). Cells were first charged to4.75 V at a current density of 0.1 mA/cm², then discharged to 2.5 V;subsequent cycles were limited to the voltage window 2.25 to 4.2 V (FIG.10). The data in FIG. 10 clearly demonstrates the principles of theinvention with respect to an iron-based electrode. During the initialcharge, lithium is extracted from the highly lithium-rich Li₅FeO₄(5Li₂O.Fe₂O₃) component of the precursor electrode (as Li₂O) andinserted into the MCMB graphite anode. On the subsequent discharge,lithium is inserted into the FePO₄ charged component of the precursorelectrode to a cut off voltage of 2.25 V, delivering a dischargecapacity of approximately 100 mAh/g, indicating the likelihood that thecharged FePO₄ component of the electrode delivered all its capacity, thetheoretical capacity of the FePO₄ component in this electrodecomposition being 88 mAh/g. The balance of the capacity (12 mAh/g) isattributed to the Fe₂O₃ component of the charged electrode derived fromLi₅FeO₄. Further capacity can be expected from these activatedLi₅FeO₄.FePO₄ electrodes if discharged to 1.5 V, when further reductionof the Fe₂O₃ component can occur, as demonstrated by the electrochemicaldata of the Li/xLi₅FeO₄.(1−x)LiFeO₂ cell shown in FIG. 9.

EXAMPLE 6

A Li_(1.2)V₃O₈ sample was synthesized by the reaction of vanadium oxidewith lithium hydroxide monohydrate for 10 h in the appropriate moleratio at 680° C. in air. The Li₅FeO₄ was made by reacting iron-oxide andlithium hydroxide monohydrate in nitrogen at 700° C. for 72 h. Alithium-ion cell was constructed in a similar fashion to that describedn in Example 5 using a 1:1 molar ratio of Li_(1.2)V₃O₈ and L_(i5)FeO₄ asthe cathode. The cell was charged to 4.9 V and then subsequentlydischarged to 2.0 V at 0.1 mA/cm² to evaluate the effectiveness of usingLi₅FeO₄ (5Li₂O.Fe₂O₃) as a source of lithium in the electrode precursorto load the MCMB graphite anode. The initial charge/discharge profile ofthis cell is shown in FIG. 11 a. The data demonstrate that during charge223 mAh/g of capacity was withdrawn from the electrode to load the MCMBanode with lithium and that 158 mAh/g was delivered by the Fe₂O₃.LiV₃O₈component formed during charge. The discharge voltage profile ischaracteristic of that expected from LiV₃O₈, and the delivered capacityis approximately 87% of the theoretical capacity value expected for theLiV₃O₈ component of the composite electrode (181 mAh/g), therebyconfirming the utility of the Li₅FeO₄.Li_(1.2) V₃O₈ precursor electrodeof this invention in a lithium-ion cell configuration. FIG. 11 b showsthe charge/discharge profiles of the cell for the subsequent sixdischarge cycles, showing the unoptimized rechargeable behavior of thelithium-iron-vanadium-oxide electrode.

This invention therefore relates to lithium-rich compounds that can beused as precursors for positive electrodes in both primary and secondary(rechargeable) lithium cells and batteries, a typical cell being shownschematically in FIG. 12, represented by the numeral 10 having anegative electrode 12 separated from a positive electrode 16 by anelectrolyte 14, all contained in an insulating housing 18 with suitableterminals (not shown) being provided in electronic contact with thenegative electrode 12 and the positive electrode 16. Binders and othermaterials normally associated with both the electrolyte and the negativeand positive electrodes are well known in the art and are not fullydescribed herein, but are included as is understood by those of ordinaryskill in this art. FIG. 13 shows a schematic illustration of one exampleof a battery in which two strings of electrochemical lithium cells,described above, are arranged in parallel, each string comprising threecells arranged in series. The invention also includes methods for makingthe lithium-rich precursor electrode compounds and methods foractivating the precursor electrodes in lithium cells and batteriesincluding the same.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.It is also understood that additional improvements in the capacity andstability of the electrodes can be expected to be made in the future byimproving and optimizing the processing techniques whereby lithium-richcompounds can be fabricated and incorporated as electrodes inelectrochemical lithium cells.

1. A positive electrode for a non-aqueous lithium cell, the electrodeincluding a precursor material comprising: (a) a first componentcontaining one or more Li₂O-containing materials; and (b) a secondcomponent containing one or more charged or partially-charged electrodematerials that can react with an integral or fractional molar quantityof lithium, based on the molecular formula of the charged material andpartially charged material respectively, during the charging anddischarging of the electrode when included in an electrochemical cell;each of the first and, second components containing lithium cations,other metal cations, and charge-balancing anions; with the proviso thatat least one of the first and second components does not containmanganese.
 2. The electrode of claim 1, wherein the first componentcomprises and intergrown or blended composite structure comprising twoor more Li₂O-containing components of different molecular structure. 3.The electrode of claim 1, wherein the metal cations of the firstcomponent comprise one or more of Mn, V, Fe and Ti cations.
 4. Theelectrode of claim 3, wherein the first component comprises one or morematerials selected from the group consisting of Li₂O.MnO₂, Li₂O.3V₂O₅,3Li₂O.V₂O₅, Li₂O.2.5Fe₂O₃, Li₂O.Fe₂O₃, 5Li₂O.Fe₂O₃, and Li₂O.TiO₂. 5.The electrode of claim 3, wherein the first component comprises one ormore materials selected from the group consisting of a Li₂MnO₃ andLiMO₂-containing material and a Li₂MnO₃ and LiM′₂O₄-containing material;wherein M and M′ are independently one or more metal cations.
 6. Theelectrode of claim 5, wherein M comprises one or more of Mn, Ni, and Co;and wherein M′ comprises Li and Mn.
 7. The electrode of claim 1, whereinthe second component comprises one or more of a metal oxide, alithium-metal-oxide, a metal phosphate and a metal sulfate.
 8. Theelectrode of claim 7, wherein the second component comprises one or moreof MnO₂, V₂O₅, Li_(1+x)V₃O₈ in which O≦x≦0.3, Fe₂O₃, Li_(1−y)FePO₄ inwhich O<y≦1, and Fe₂(SO₄)₃.
 9. The electrode of claim 1, wherein firstcomponent comprises one or more materials selected from the groupconsisting of Li₂O.MnO₂, Li₂O.3V₂O₅, 3Li₂O.V₂O₅, Li₂O.2.5Fe₂O₃,Li₂O.Fe₂O₃, 5Li₂O.Fe₂O₃, and Li₂O.TiO₂; and the second componentcomprises one or more of MnO₂, V₂O₅, Li_(1+x) V₃O₈ in which 0≦x≦0.3,Fe₂O₃, Li_(1−y)FePO₄ in which 0<y≦1, and Fe₂(SO₄)₃.
 10. The electrode ofclaim 1, wherein the metal cations of the first component comprise oneor more of Mn, V, Fe and Ti; and the second component comprises one ormore of a metal oxide, a lithium-metal-oxide, a metal phosphate and ametal sulfate.
 11. A method of activating the positive electrode ofclaim 1 comprising either (a) applying a sufficiently high potential tothe positive electrode in an electrochemical cell also including anegative electrode and a non-aqueous electrolyte to remove Li₂O from theelectrode, or (b) reacting the precursor material with an acidicsolution having a 0<pH<7 to remove Li₂O from the precursor material. 12.The method of claim 11, wherein the positive electrode is activated inthe electrochemical cell whereby the Li₂O removed from the positiveelectrode in the electrochemical cell loads lithium into the negativeelectrode of the cell.
 13. The method of claim 12, wherein the negativeelectrode of the electrochemical cell comprises one or more of a carbonmaterial, a metal material, a semi-metal material, an intermetallicmaterial, and a metal oxide material.
 14. The method of claim 13,wherein the negative electrode of the electrochemical cell comprises oneor more of graphite, Sn, Si, Cu₆Sn₅, and Li₄Ti₅O₁₂.
 15. The method ofclaim 11, wherein the positive electrode is activated by reacting theprecursor material with an acid comprising HF, HCl, HNO₃ or H₃PO₄. 16.An activated electrode made according to the method of claim
 11. 17. Theactivated electrode of 16, wherein the electrode is either crystalline,partially crystalline, or amorphous.
 18. A non-aqueous lithiumelectrochemical cell comprising a negative electrode, an electrolyte,and a positive electrode; the positive electrode including a precursormaterial comprising: (a) a first component containing one or moreLi₂O-containing materials; and (b) a second component containing one ormore charged or partially-charged electrode materials that can reactwith an integral or fractional molar quantity of lithium, based on themolecular formula of the charged material and partially charged materialrespectively, during the charging and discharging of the electrode whenincluded in an electrochemical cell; each of the first and, secondcomponents containing lithium cations, other metal cations, andcharge-balancing anions; with the proviso that at least one of the firstand second components does not contain manganese.
 19. The non-aqueouslithium electrochemical cell of claim 18, wherein the positive electrodehas been activated by removing Li₂O from the precursor material.
 20. Anon-aqueous lithium battery comprising a plurality of electricallyconnected electrochemical cells, each electrochemical cell including anegative electrode, an electrolyte, and a positive electrode; thepositive electrode including a precursor material comprising: (a) afirst component containing one or more Li₂O-containing materials; and(b) a second component containing one or more charged orpartially-charged electrode materials that can react with an integral orfractional molar quantity of lithium, based on the molecular formula ofthe charged material and partially charged material respectively, duringthe charging and discharging of the electrode when included in anelectrochemical cell; each of the first and, second componentscontaining lithium cations, other metal cations, and charge-balancinganions; with the proviso that at least one of the first and secondcomponents does not contain manganese.
 21. The non-aqueous lithiumbattery of claim 20, wherein the positive electrodes of the cells havebeen activated by removing Li₂O from the precursor materials.